Instead of applying a transform for every RenderObject, pass down an Offset for where to paint.

sky/sdk/lib/widgets/tabs.dart

Index: sky/sdk/lib/widgets/tabs.dart
diff --git a/sky/sdk/lib/widgets/tabs.dart b/sky/sdk/lib/widgets/tabs.dart
index 09d03be9df8a2b0fa35f882b0701c291a97318b1..1edc4fe2dbae7faf381d3f810abcb4064a28bd7f 100644
--- a/sky/sdk/lib/widgets/tabs.dart
+++ b/sky/sdk/lib/widgets/tabs.dart
@@ -131,21 +131,22 @@ class RenderTabBar extends RenderBox with
     defaultHitTestChildren(result, position: position);
   }
 
-  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab) {
+  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab, Offset offset) {
     if (indicatorColor == null)
       return;
 
     var size = new Size(selectedTab.size.width, _kTabIndicatorHeight);
     var point = new Point(
       selectedTab.parentData.position.x,
-      _tabBarHeight - _kTabIndicatorHeight);
-    Rect rect = new Rect.fromPointAndSize(point, size);
+      _tabBarHeight - _kTabIndicatorHeight
+    );
+    Rect rect = new Rect.fromPointAndSize(point + offset, size);
     canvas.drawRect(rect, new Paint()..color = indicatorColor);
   }
 
-  void paint(RenderCanvas canvas) {
+  void paint(RenderCanvas canvas, Offset offset) {
     if (backgroundColor != null) {
-      Rect rect = new Rect.fromSize(size);
+      Rect rect = offset + size;
       canvas.drawRect(rect, new Paint()..color = backgroundColor);
     }
 
@@ -153,9 +154,9 @@ class RenderTabBar extends RenderBox with
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is TabBarParentData);
-      canvas.paintChild(child, child.parentData.position);
+      canvas.paintChild(child, child.parentData.position + offset);
       if (index++ == selectedIndex)
-        _paintIndicator(canvas, child);
+        _paintIndicator(canvas, child, offset);
       child = child.parentData.nextSibling;
     }
   }